<?php

$a = 5;
$b = 6;

$a = $a + $b;//11 = 5 + 6
$b = $a - $b;//5  = 11 - 6
$a = $a - $b;//6  = 11 - 5

echo "a ==> $a" , "\n\n", "b ==> $b","\n\n";
